1
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Kolbin D, Walker BL, Hult C, Stanton JD, Adalsteinsson D, Forest MG, Bloom K. Polymer Modeling Reveals Interplay between Physical Properties of Chromosomal DNA and the Size and Distribution of Condensin-Based Chromatin Loops. Genes (Basel) 2023; 14:2193. [PMID: 38137015 PMCID: PMC10742461 DOI: 10.3390/genes14122193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 11/28/2023] [Accepted: 12/06/2023] [Indexed: 12/24/2023] Open
Abstract
Transient DNA loops occur throughout the genome due to thermal fluctuations of DNA and the function of SMC complex proteins such as condensin and cohesin. Transient crosslinking within and between chromosomes and loop extrusion by SMCs have profound effects on high-order chromatin organization and exhibit specificity in cell type, cell cycle stage, and cellular environment. SMC complexes anchor one end to DNA with the other extending some distance and retracting to form a loop. How cells regulate loop sizes and how loops distribute along chromatin are emerging questions. To understand loop size regulation, we employed bead-spring polymer chain models of chromatin and the activity of an SMC complex on chromatin. Our study shows that (1) the stiffness of the chromatin polymer chain, (2) the tensile stiffness of chromatin crosslinking complexes such as condensin, and (3) the strength of the internal or external tethering of chromatin chains cooperatively dictate the loop size distribution and compaction volume of induced chromatin domains. When strong DNA tethers are invoked, loop size distributions are tuned by condensin stiffness. When DNA tethers are released, loop size distributions are tuned by chromatin stiffness. In this three-way interaction, the presence and strength of tethering unexpectedly dictates chromatin conformation within a topological domain.
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Affiliation(s)
- Daniel Kolbin
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (D.K.); (J.D.S.)
| | - Benjamin L. Walker
- Department of Mathematics, University of California-Irvine, Irvine, CA 92697, USA;
| | - Caitlin Hult
- Department of Mathematics, Gettysburg College, Gettysburg, PA 17325, USA
| | - John Donoghue Stanton
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (D.K.); (J.D.S.)
| | - David Adalsteinsson
- Department of Mathematics and Carolina Center for Interdisciplinary Applied Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (D.A.); (M.G.F.)
| | - M. Gregory Forest
- Department of Mathematics and Carolina Center for Interdisciplinary Applied Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (D.A.); (M.G.F.)
- Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; (D.K.); (J.D.S.)
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2
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González L, Kolbin D, Trahan C, Jeronimo C, Robert F, Oeffinger M, Bloom K, Michnick SW. Adaptive partitioning of a gene locus to the nuclear envelope in Saccharomyces cerevisiae is driven by polymer-polymer phase separation. Nat Commun 2023; 14:1135. [PMID: 36854718 PMCID: PMC9975218 DOI: 10.1038/s41467-023-36391-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Accepted: 01/30/2023] [Indexed: 03/03/2023] Open
Abstract
Partitioning of active gene loci to the nuclear envelope (NE) is a mechanism by which organisms increase the speed of adaptation and metabolic robustness to fluctuating resources in the environment. In the yeast Saccharomyces cerevisiae, adaptation to nutrient depletion or other stresses, manifests as relocalization of active gene loci from nucleoplasm to the NE, resulting in more efficient transport and translation of mRNA. The mechanism by which this partitioning occurs remains a mystery. Here, we demonstrate that the yeast inositol depletion-responsive gene locus INO1 partitions to the nuclear envelope, driven by local histone acetylation-induced polymer-polymer phase separation from the nucleoplasmic phase. This demixing is consistent with recent evidence for chromatin phase separation by acetylation-mediated dissolution of multivalent histone association and fits a physical model where increased bending stiffness of acetylated chromatin polymer causes its phase separation from de-acetylated chromatin. Increased chromatin spring stiffness could explain nucleation of transcriptional machinery at active gene loci.
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Affiliation(s)
- Lidice González
- Département de Biochimie, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, QC, H3C 3J7, Canada
| | - Daniel Kolbin
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Christian Trahan
- Institut de recherches cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC, H2W 1R7, Canada
| | - Célia Jeronimo
- Institut de recherches cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC, H2W 1R7, Canada
| | - François Robert
- Institut de recherches cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC, H2W 1R7, Canada
- Faculty of Medicine, Division of Experimental Medicine, McGill University, Montréal, QC, H3A 1A3, Canada
- Département de Médecine, Faculté de Médecine, Université de Montréal, 2900 Boul. Édouard-Montpetit, Montréal, QC, H3T 1J4, Canada
| | - Marlene Oeffinger
- Département de Biochimie, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, QC, H3C 3J7, Canada
- Institut de recherches cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC, H2W 1R7, Canada
- Faculty of Medicine, Division of Experimental Medicine, McGill University, Montréal, QC, H3A 1A3, Canada
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Stephen W Michnick
- Département de Biochimie, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, QC, H3C 3J7, Canada.
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3
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Lawrimore J, de Larminat SC, Cook D, Friedman B, Doshi A, Yeh E, Bloom K. Polymer models reveal how chromatin modification can modulate force at the kinetochore. Mol Biol Cell 2022; 33:ar97. [PMID: 35704466 DOI: 10.1091/mbc.e22-02-0041] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A key feature of chromosome segregation is the ability to sense tension between sister kinetochores. DNA between sister kinetochores must be packaged in a way that sustains tension propagation from one kinetochore to its sister, approximately 1 micron away. A molecular bottlebrush consisting of a primary axis populated with a crowded array of side chains provides a means to build tension over length scales considerably larger than the stiffness of the individual elements, that is, DNA polymer. Evidence for the bottlebrush organization of chromatin between sister kinetochores comes from genetic, cell biological, and polymer modeling of the budding yeast centromere. In this study, we have used polymer dynamic simulations of the bottlebrush to recapitulate experimental observations of kinetochore structure. Several aspects of the spatial distribution of kinetochore proteins and their response to perturbation lack a mechanistic understanding. Changes in physical parameters of bottlebrush, DNA stiffness, and DNA loops directly impact the architecture of the inner kinetochore. This study reveals that the bottlebrush is an active participant in building tension between sister kinetochores and proposes a mechanism for chromatin feedback to the kinetochore.
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Affiliation(s)
- Josh Lawrimore
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Solenn C de Larminat
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Diana Cook
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Brandon Friedman
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Ayush Doshi
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Elaine Yeh
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Kerry Bloom
- Biology Department, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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4
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Locatelli M, Lawrimore J, Lin H, Sanaullah S, Seitz C, Segall D, Kefer P, Salvador Moreno N, Lietz B, Anderson R, Holmes J, Yuan C, Holzwarth G, Bloom KS, Liu J, Bonin K, Vidi PA. DNA damage reduces heterogeneity and coherence of chromatin motions. Proc Natl Acad Sci U S A 2022; 119:e2205166119. [PMID: 35858349 PMCID: PMC9304018 DOI: 10.1073/pnas.2205166119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 06/07/2022] [Indexed: 01/14/2023] Open
Abstract
Chromatin motions depend on and may regulate genome functions, in particular the DNA damage response. In yeast, DNA double-strand breaks (DSBs) globally increase chromatin diffusion, whereas in higher eukaryotes the impact of DSBs on chromatin dynamics is more nuanced. We mapped the motions of chromatin microdomains in mammalian cells using diffractive optics and photoactivatable chromatin probes and found a high level of spatial heterogeneity. DNA damage reduces heterogeneity and imposes spatially defined shifts in motions: Distal to DNA breaks, chromatin motions are globally reduced, whereas chromatin retains higher mobility at break sites. These effects are driven by context-dependent changes in chromatin compaction. Photoactivated lattices of chromatin microdomains are ideal to quantify microscale coupling of chromatin motion. We measured correlation distances up to 2 µm in the cell nucleus, spanning chromosome territories, and speculate that this correlation distance between chromatin microdomains corresponds to the physical separation of A and B compartments identified in chromosome conformation capture experiments. After DNA damage, chromatin motions become less correlated, a phenomenon driven by phase separation at DSBs. Our data indicate tight spatial control of chromatin motions after genomic insults, which may facilitate repair at the break sites and prevent deleterious contacts of DSBs, thereby reducing the risk of genomic rearrangements.
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Affiliation(s)
- Maëlle Locatelli
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Hua Lin
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
| | - Sarvath Sanaullah
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Clayton Seitz
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
| | - Dave Segall
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Paul Kefer
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Naike Salvador Moreno
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Benton Lietz
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Rebecca Anderson
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Julia Holmes
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Chongli Yuan
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907
| | - George Holzwarth
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Kerry S. Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jing Liu
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
- Melvin and Bren Simon Comprehensive Cancer Center, Indiana University, Indianapolis, IN 46202
- Center for Computational Biology and Bioinformatics, Indiana University, Indianapolis, IN 46202
| | - Keith Bonin
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
- Atrium Health Wake Forest Baptist Comprehensive Cancer Center, Winston-Salem, NC 27157
| | - Pierre-Alexandre Vidi
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
- Atrium Health Wake Forest Baptist Comprehensive Cancer Center, Winston-Salem, NC 27157
- Laboratoire InGenO, Institut de Cancérologie de l’Ouest, 49055 Angers, France
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5
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Abstract
The centromere serves as the binding site for the kinetochore and is essential for the faithful segregation of chromosomes throughout cell division. The point centromere in yeast is encoded by a ∼115 bp specific DNA sequence, whereas regional centromeres range from 6-10 kbp in fission yeast to 5-10 Mbp in humans. Understanding the physical structure of centromere chromatin (pericentromere in yeast), defined as the chromatin between sister kinetochores, will provide fundamental insights into how centromere DNA is woven into a stiff spring that is able to resist microtubule pulling forces during mitosis. One hallmark of the pericentromere is the enrichment of the structural maintenance of chromosome (SMC) proteins cohesin and condensin. Based on studies from population approaches (ChIP-seq and Hi-C) and experimentally obtained images of fluorescent probes of pericentromeric structure, as well as quantitative comparisons between simulations and experimental results, we suggest a mechanism for building tension between sister kinetochores. We propose that the centromere is a chromatin bottlebrush that is organized by the loop-extruding proteins condensin and cohesin. The bottlebrush arrangement provides a biophysical means to transform pericentromeric chromatin into a spring due to the steric repulsion between radial loops. We argue that the bottlebrush is an organizing principle for chromosome organization that has emerged from multiple approaches in the field.
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6
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Mach P, Kos PI, Zhan Y, Cramard J, Gaudin S, Tünnermann J, Marchi E, Eglinger J, Zuin J, Kryzhanovska M, Smallwood S, Gelman L, Roth G, Nora EP, Tiana G, Giorgetti L. Cohesin and CTCF control the dynamics of chromosome folding. Nat Genet 2022; 54:1907-1918. [PMID: 36471076 PMCID: PMC9729113 DOI: 10.1038/s41588-022-01232-7] [Citation(s) in RCA: 50] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 10/19/2022] [Indexed: 12/12/2022]
Abstract
In mammals, interactions between sequences within topologically associating domains enable control of gene expression across large genomic distances. Yet it is unknown how frequently such contacts occur, how long they last and how they depend on the dynamics of chromosome folding and loop extrusion activity of cohesin. By imaging chromosomal locations at high spatial and temporal resolution in living cells, we show that interactions within topologically associating domains are transient and occur frequently during the course of a cell cycle. Interactions become more frequent and longer in the presence of convergent CTCF sites, resulting in suppression of variability in chromosome folding across time. Supported by physical models of chromosome dynamics, our data suggest that CTCF-anchored loops last around 10 min. Our results show that long-range transcriptional regulation might rely on transient physical proximity, and that cohesin and CTCF stabilize highly dynamic chromosome structures, facilitating selected subsets of chromosomal interactions.
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Affiliation(s)
- Pia Mach
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland ,grid.6612.30000 0004 1937 0642University of Basel, Basel, Switzerland
| | - Pavel I. Kos
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Yinxiu Zhan
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Julie Cramard
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Simon Gaudin
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland ,grid.15140.310000 0001 2175 9188École Normale Supérieure de Lyon, Lyon, France ,grid.7849.20000 0001 2150 7757Université Claude Bernard Lyon I, Lyon, France
| | - Jana Tünnermann
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland ,grid.6612.30000 0004 1937 0642University of Basel, Basel, Switzerland
| | - Edoardo Marchi
- grid.4708.b0000 0004 1757 2822Università degli Studi di Milano, Milan, Italy ,grid.6045.70000 0004 1757 5281INFN, Milan, Italy
| | - Jan Eglinger
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Jessica Zuin
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Mariya Kryzhanovska
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Sebastien Smallwood
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Laurent Gelman
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Gregory Roth
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Elphège P. Nora
- grid.266102.10000 0001 2297 6811Cardiovascular Research Institute, University of California San Francisco, San Francisco, CA USA ,grid.266102.10000 0001 2297 6811Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, CA USA
| | - Guido Tiana
- grid.4708.b0000 0004 1757 2822Università degli Studi di Milano, Milan, Italy ,grid.6045.70000 0004 1757 5281INFN, Milan, Italy
| | - Luca Giorgetti
- grid.482245.d0000 0001 2110 3787Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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7
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Kefer P, Iqbal F, Locatelli M, Lawrimore J, Zhang M, Bloom K, Bonin K, Vidi PA, Liu J. Performance of deep learning restoration methods for the extraction of particle dynamics in noisy microscopy image sequences. Mol Biol Cell 2021; 32:903-914. [PMID: 33502895 PMCID: PMC8108534 DOI: 10.1091/mbc.e20-11-0689] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Particle tracking in living systems requires low light exposure and short exposure times to avoid phototoxicity and photobleaching and to fully capture particle motion with high-speed imaging. Low-excitation light comes at the expense of tracking accuracy. Image restoration methods based on deep learning dramatically improve the signal-to-noise ratio in low-exposure data sets, qualitatively improving the images. However, it is not clear whether images generated by these methods yield accurate quantitative measurements such as diffusion parameters in (single) particle tracking experiments. Here, we evaluate the performance of two popular deep learning denoising software packages for particle tracking, using synthetic data sets and movies of diffusing chromatin as biological examples. With synthetic data, both supervised and unsupervised deep learning restored particle motions with high accuracy in two-dimensional data sets, whereas artifacts were introduced by the denoisers in three-dimensional data sets. Experimentally, we found that, while both supervised and unsupervised approaches improved tracking results compared with the original noisy images, supervised learning generally outperformed the unsupervised approach. We find that nicer-looking image sequences are not synonymous with more precise tracking results and highlight that deep learning algorithms can produce deceiving artifacts with extremely noisy images. Finally, we address the challenge of selecting parameters to train convolutional neural networks by implementing a frugal Bayesian optimizer that rapidly explores multidimensional parameter spaces, identifying networks yielding optimal particle tracking accuracy. Our study provides quantitative outcome measures of image restoration using deep learning. We anticipate broad application of this approach to critically evaluate artificial intelligence solutions for quantitative microscopy.
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Affiliation(s)
- Paul Kefer
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Fadil Iqbal
- Department of Physics, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202
| | - Maelle Locatelli
- Department of Cancer Biology, Wake Forest School of Medicine, and
| | - Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Mengdi Zhang
- Department of Physics, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202.,Department of Pharmacology, School of Pharmacy, Harbin Medical University, Harbin 150081, China
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Keith Bonin
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109.,Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC 27157
| | - Pierre-Alexandre Vidi
- Department of Cancer Biology, Wake Forest School of Medicine, and.,Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC 27157
| | - Jing Liu
- Department of Physics, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202
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8
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He Y, Lawrimore J, Cook D, Van Gorder EE, De Larimat SC, Adalsteinsson D, Forest MG, Bloom K. Statistical mechanics of chromosomes: in vivo and in silico approaches reveal high-level organization and structure arise exclusively through mechanical feedback between loop extruders and chromatin substrate properties. Nucleic Acids Res 2020; 48:11284-11303. [PMID: 33080019 PMCID: PMC7672462 DOI: 10.1093/nar/gkaa871] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 09/22/2020] [Accepted: 09/24/2020] [Indexed: 11/14/2022] Open
Abstract
The revolution in understanding higher order chromosome dynamics and organization derives from treating the chromosome as a chain polymer and adapting appropriate polymer-based physical principles. Using basic principles, such as entropic fluctuations and timescales of relaxation of Rouse polymer chains, one can recapitulate the dominant features of chromatin motion observed in vivo. An emerging challenge is to relate the mechanical properties of chromatin to more nuanced organizational principles such as ubiquitous DNA loops. Toward this goal, we introduce a real-time numerical simulation model of a long chain polymer in the presence of histones and condensin, encoding physical principles of chromosome dynamics with coupled histone and condensin sources of transient loop generation. An exact experimental correlate of the model was obtained through analysis of a model-matching fluorescently labeled circular chromosome in live yeast cells. We show that experimentally observed chromosome compaction and variance in compaction are reproduced only with tandem interactions between histone and condensin, not from either individually. The hierarchical loop structures that emerge upon incorporation of histone and condensin activities significantly impact the dynamic and structural properties of chromatin. Moreover, simulations reveal that tandem condensin–histone activity is responsible for higher order chromosomal structures, including recently observed Z-loops.
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Affiliation(s)
- Yunyan He
- Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Diana Cook
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | | | | | - David Adalsteinsson
- Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - M Gregory Forest
- Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.,Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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9
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Abstract
The kinetochore is a complex structure whose function is absolutely essential. Unlike the centromere, the kinetochore at first appeared remarkably well conserved from yeast to humans, especially the microtubule-binding outer kinetochore. However, recent efforts towards biochemical reconstitution of diverse kinetochores challenge the notion of a similarly conserved architecture for the constitutively centromere-associated network of the inner kinetochore. This review briefly summarizes the evidence from comparative genomics for interspecific variability in inner kinetochore composition and focuses on novel biochemical evidence indicating that even homologous inner kinetochore protein complexes are put to different uses in different organisms.
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Affiliation(s)
- G E Hamilton
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - T N Davis
- Department of Biochemistry, University of Washington, Seattle, WA, USA
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10
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Lawrimore CJ, Lawrimore J, He Y, Chavez S, Bloom K. Polymer perspective of genome mobilization. Mutat Res 2020; 821:111706. [PMID: 32516654 DOI: 10.1016/j.mrfmmm.2020.111706] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 04/30/2020] [Accepted: 05/06/2020] [Indexed: 02/07/2023]
Abstract
Chromosome motion is an intrinsic feature of all DNA-based metabolic processes and is a particularly well-documented response to both DNA damage and repair. By using both biological and polymer physics approaches, many of the contributing factors of chromatin motility have been elucidated. These include the intrinsic properties of chromatin, such as stiffness, as well as the loop modulators condensin and cohesin. Various biological factors such as external tethering to nuclear domains, ATP-dependent processes, and nucleofilaments further impact chromatin motion. DNA damaging agents that induce double-stranded breaks also cause increased chromatin motion that is modulated by recruitment of repair and checkpoint proteins. Approaches that integrate biological experimentation in conjunction with models from polymer physics provide mechanistic insights into the role of chromatin dynamics in biological function. In this review we discuss the polymer models and the effects of both DNA damage and repair on chromatin motion as well as mechanisms that may underlie these effects.
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Affiliation(s)
- Colleen J Lawrimore
- Department of Biology, 623 Fordham Hall CB#3280, University of North Carolina, Chapel Hill, NC 27599-3280, United States
| | - Josh Lawrimore
- Department of Biology, 623 Fordham Hall CB#3280, University of North Carolina, Chapel Hill, NC 27599-3280, United States
| | - Yunyan He
- Department of Biology, 623 Fordham Hall CB#3280, University of North Carolina, Chapel Hill, NC 27599-3280, United States
| | - Sergio Chavez
- Department of Biology, 623 Fordham Hall CB#3280, University of North Carolina, Chapel Hill, NC 27599-3280, United States
| | - Kerry Bloom
- Department of Biology, 623 Fordham Hall CB#3280, University of North Carolina, Chapel Hill, NC 27599-3280, United States.
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11
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Abstract
Both the pericentromere and the nucleolus have unique characteristics that distinguish them amongst the rest of genome. Looping of pericentromeric DNA, due to structural maintenance of chromosome (SMC) proteins condensin and cohesin, drives its ability to maintain tension during metaphase. Similar loops are formed via condensin and cohesin in nucleolar ribosomal DNA (rDNA). Condensin and cohesin are also concentrated in transfer RNA (tRNA) genes, genes which may be located within the pericentromere as well as tethered to the nucleolus. Replication fork stalling, as well as downstream consequences such as genomic recombination, are characteristic of both the pericentromere and rDNA. Furthermore, emerging evidence suggests that the pericentromere may function as a liquid-liquid phase separated domain, similar to the nucleolus. We therefore propose that the pericentromere and nucleolus, in part due to their enrichment of SMC proteins and others, contain similar domains that drive important cellular activities such as segregation, stability, and repair.
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Affiliation(s)
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA;
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12
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Brahmachari S, Marko JF. Chromosome disentanglement driven via optimal compaction of loop-extruded brush structures. Proc Natl Acad Sci U S A 2019; 116:24956-65. [PMID: 31757850 DOI: 10.1073/pnas.1906355116] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Eukaryote cell division features a chromosome compaction-decompaction cycle that is synchronized with their physical and topological segregation. It has been proposed that lengthwise compaction of chromatin into mitotic chromosomes via loop extrusion underlies the compaction-segregation/resolution process. We analyze this disentanglement scheme via considering the chromosome to be a succession of DNA/chromatin loops-a polymer "brush"-where active extrusion of loops controls the brush structure. Given type-II DNA topoisomerase (Topo II)-catalyzed topology fluctuations, we find that interchromosome entanglements are minimized for a certain "optimal" loop that scales with the chromosome size. The optimal loop organization is in accord with experimental data across species, suggesting an important structural role of genomic loops in maintaining a less entangled genome. Application of the model to the interphase genome indicates that active loop extrusion can maintain a level of chromosome compaction with suppressed entanglements; the transition to the metaphase state requires higher lengthwise compaction and drives complete topological segregation. Optimized genomic loops may provide a means for evolutionary propagation of gene-expression patterns while simultaneously maintaining a disentangled genome. We also find that compact metaphase chromosomes have a densely packed core along their cylindrical axes that explains their observed mechanical stiffness. Our model connects chromosome structural reorganization to topological resolution through the cell cycle and highlights a mechanism of directing Topo II-mediated strand passage via loop extrusion-driven lengthwise compaction.
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13
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Abstract
The rise of machine learning and deep learning technologies have allowed researchers to automate image classification. We describe a method that incorporates automated image classification and principal component analysis to evaluate computational models of biological structures. We use a computational model of the kinetochore to demonstrate our artificial-intelligence (AI)-assisted modeling method. The kinetochore is a large protein complex that connects chromosomes to the mitotic spindle to facilitate proper cell division. The kinetochore can be divided into two regions: the inner kinetochore, including proteins that interact with DNA; and the outer kinetochore, comprised of microtubule-binding proteins. These two kinetochore regions have been shown to have different distributions during metaphase in live budding yeast and therefore act as a test case for our forward modeling technique. We find that a simple convolutional neural net (CNN) can correctly classify fluorescent images of inner and outer kinetochore proteins and show a CNN trained on simulated, fluorescent images can detect difference in experimental images. A polymer model of the ribosomal DNA locus serves as a second test for the method. The nucleolus surrounds the ribosomal DNA locus and appears amorphous in live-cell, fluorescent microscopy experiments in budding yeast, making detection of morphological changes challenging. We show a simple CNN can detect subtle differences in simulated images of the ribosomal DNA locus, demonstrating our CNN-based classification technique can be used on a variety of biological structures.
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Affiliation(s)
- Josh Lawrimore
- Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Ayush Doshi
- Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Benjamin Walker
- Department of Mathematics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Kerry Bloom
- Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
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14
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Lawrimore J, Bloom K. The regulation of chromosome segregation via centromere loops. Crit Rev Biochem Mol Biol 2019; 54:352-370. [PMID: 31573359 PMCID: PMC6856439 DOI: 10.1080/10409238.2019.1670130] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 09/02/2019] [Accepted: 09/17/2019] [Indexed: 12/14/2022]
Abstract
Biophysical studies of the yeast centromere have shown that the organization of the centromeric chromatin plays a crucial role in maintaining proper tension between sister kinetochores during mitosis. While centromeric chromatin has traditionally been considered a simple spring, recent work reveals the centromere as a multifaceted, tunable shock absorber. Centromeres can differ from other regions of the genome in their heterochromatin state, supercoiling state, and enrichment of structural maintenance of chromosomes (SMC) protein complexes. Each of these differences can be utilized to alter the effective stiffness of centromeric chromatin. In budding yeast, the SMC protein complexes condensin and cohesin stiffen chromatin by forming and cross-linking chromatin loops, respectively, into a fibrous structure resembling a bottlebrush. The high density of the loops compacts chromatin while spatially isolating the tension from spindle pulling forces to a subset of the chromatin. Paradoxically, the molecular crowding of chromatin via cohesin and condensin also causes an outward/poleward force. The structure allows the centromere to act as a shock absorber that buffers the variable forces generated by dynamic spindle microtubules. Based on the distribution of SMCs from bacteria to human and the conserved distance between sister kinetochores in a wide variety of organisms (0.4 to 1 micron), we propose that the bottlebrush mechanism is the foundational principle for centromere function in eukaryotes.
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Affiliation(s)
- Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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15
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Kouznetsova A, Kitajima TS, Brismar H, Höög C. Post-metaphase correction of aberrant kinetochore-microtubule attachments in mammalian eggs. EMBO Rep 2019; 20:e47905. [PMID: 31290587 PMCID: PMC6680117 DOI: 10.15252/embr.201947905] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 05/24/2019] [Accepted: 06/07/2019] [Indexed: 12/29/2022] Open
Abstract
The accuracy of the two sequential meiotic divisions in oocytes is essential for creating a haploid gamete with a normal chromosomal content. Here, we have analysed the 3D dynamics of chromosomes during the second meiotic division in live mouse oocytes. We find that chromosomes form stable kinetochore-microtubule attachments at the end of prometaphase II stage that are retained until anaphase II onset. Remarkably, we observe that more than 20% of the kinetochore-microtubule attachments at the metaphase II stage are merotelic or lateral. However, < 1% of all chromosomes at onset of anaphase II are found to lag at the spindle equator and < 10% of the laggards missegregate and give rise to aneuploid gametes. Our results demonstrate that aberrant kinetochore-microtubule attachments are not corrected at the metaphase stage of the second meiotic division. Thus, the accuracy of the chromosome segregation process in mouse oocytes during meiosis II is ensured by an efficient correction process acting at the anaphase stage.
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Affiliation(s)
- Anna Kouznetsova
- Department of Cell and Molecular BiologyKarolinska InstitutetStockholmSweden
| | - Tomoya S Kitajima
- Laboratory for Chromosome SegregationRIKEN Center for Biosystems Dynamics ResearchKobeJapan
| | - Hjalmar Brismar
- Science for Life LaboratoryDepartment of Applied PhysicsRoyal Institute of TechnologySolnaSweden
| | - Christer Höög
- Department of Cell and Molecular BiologyKarolinska InstitutetStockholmSweden
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16
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Harasymiw LA, Tank D, McClellan M, Panigrahy N, Gardner MK. Centromere mechanical maturation during mammalian cell mitosis. Nat Commun 2019; 10:1761. [PMID: 30988289 DOI: 10.1038/s41467-019-09578-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 03/13/2019] [Indexed: 12/30/2022] Open
Abstract
During mitosis, tension develops across the centromere as a result of spindle-based forces. Metaphase tension may be critical in preventing mitotic chromosome segregation errors, however, the nature of force transmission at the centromere and the role of centromere mechanics in controlling metaphase tension remains unknown. We combined quantitative, biophysical microscopy with computational analysis to elucidate the mechanics of the centromere in unperturbed, mitotic human cells. We discovered that the mechanical stiffness of the human centromere matures during mitotic progression, which leads to amplified centromere tension specifically at metaphase. Centromere mechanical maturation is disrupted across multiple aneuploid cell lines, leading to a weak metaphase tension signal. Further, increasing deficiencies in centromere mechanical maturation are correlated with rising frequencies of lagging, merotelic chromosomes in anaphase, leading to segregation defects at telophase. Thus, we reveal a centromere maturation process that may be critical to the fidelity of chromosome segregation during mitosis. During mitosis, tension at the centromere occurs from the spindle but the role of centromere mechanics in controlling metaphase tension is poorly understood. Here, the authors report that mechanical stiffnness of the centromere matures during mitotic progression and is amplified specifically at metaphase.
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17
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Abstract
Our understanding of higher order chromosome structure has been transformed through statistical mechanics-based computer simulations of polymer chains. A new study exploring basic electrostatic interactions demystifies how chromosomes regulate their state of compaction over several orders of magnitude.
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Affiliation(s)
- Kerry Bloom
- Department of Biology, University of North Carolina, Chapel Hill, NC, USA.
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18
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Abstract
Condensins and cohesins are highly conserved complexes that tether together DNA loci within a single DNA molecule to produce DNA loops. Condensin and cohesin structures, however, are different, and the DNA loops produced by each underlie distinct cell processes. Condensin rods compact chromosomes during mitosis, with condensin I and II complexes producing spatially defined and nested looping in metazoan cells. Structurally adaptive cohesin rings produce loops, which organize the genome during interphase. Cohesin-mediated loops, termed topologically associating domains or TADs, antagonize the formation of epigenetically defined but untethered DNA volumes, termed compartments. While condensin complexes formed through cis-interactions must maintain chromatin compaction throughout mitosis, cohesins remain highly dynamic during interphase to allow for transcription-mediated responses to external cues and the execution of developmental programs. Here, I review differences in condensin and cohesin structures, and highlight recent advances regarding the intramolecular or cis-based tetherings through which condensins compact DNA during mitosis and cohesins organize the genome during interphase.
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Affiliation(s)
- Robert V Skibbens
- Department of Biological Sciences, 111 Research Drive, Lehigh University, Bethlehem, PA 18015, USA
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19
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Abstract
Chromatin dynamics and organization can be altered by condensin complexes. In turn, the molecular behavior of a condensin complex changes based on the tension of the substrate to which condensin is bound. This interplay between chromatin organization and condensin behavior demonstrates the need for tools that allows condensin complexes to be observed on a variety of chromatin organizations. We provide a method for simulating condensin complexes on a dynamic polymer substrate using the polymer dynamics simulator ChromoShake and the condensin simulator RotoStep. These simulations can be converted into simulated fluorescent images that are able to be directly compared to experimental images of condensin and fluorescently labeled chromatin. Our pipeline enables users to explore how changes in condensin behavior alters chromatin dynamics and vice versa while providing simulated image datasets that can be directly compared to experimental observations.
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Affiliation(s)
- Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, NC 27599, USA,Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, NC 27599, USA
| | - Yunyan He
- Department of Mathematics and Biomedical Engineering, University of North Carolina at Chapel Hill, NC 27599, USA
| | - M. Gregory Forest
- Department of Mathematics and Biomedical Engineering, University of North Carolina at Chapel Hill, NC 27599, USA
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, NC 27599, USA
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20
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Cook DM, Bennett M, Friedman B, Lawrimore J, Yeh E, Bloom K. Fork pausing allows centromere DNA loop formation and kinetochore assembly. Proc Natl Acad Sci U S A 2018; 115:11784-11789. [PMID: 30373818 PMCID: PMC6243264 DOI: 10.1073/pnas.1806791115] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
De novo kinetochore assembly, but not template-directed assembly, is dependent on COMA, the kinetochore complex engaged in cohesin recruitment. The slowing of replication fork progression by treatment with phleomycin (PHL), hydroxyurea, or deletion of the replication fork protection protein Csm3 can activate de novo kinetochore assembly in COMA mutants. Centromere DNA looping at the site of de novo kinetochore assembly can be detected shortly after exposure to PHL. Using simulations to explore the thermodynamics of DNA loops, we propose that loop formation is disfavored during bidirectional replication fork migration. One function of replication fork stalling upon encounters with DNA damage or other blockades may be to allow time for thermal fluctuations of the DNA chain to explore numerous configurations. Biasing thermodynamics provides a mechanism to facilitate macromolecular assembly, DNA repair, and other nucleic acid transactions at the replication fork. These loop configurations are essential for sister centromere separation and kinetochore assembly in the absence of the COMA complex.
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Affiliation(s)
- Diana M Cook
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
| | - Maggie Bennett
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
| | - Brandon Friedman
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
| | - Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
| | - Elaine Yeh
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
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21
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Lawrimore J, Doshi A, Friedman B, Yeh E, Bloom K. Geometric partitioning of cohesin and condensin is a consequence of chromatin loops. Mol Biol Cell 2018; 29:2737-2750. [PMID: 30207827 PMCID: PMC6249845 DOI: 10.1091/mbc.e18-02-0131] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 08/13/2018] [Accepted: 09/04/2018] [Indexed: 12/29/2022] Open
Abstract
SMC (structural maintenance of chromosomes) complexes condensin and cohesin are crucial for proper chromosome organization. Condensin has been reported to be a mechanochemical motor capable of forming chromatin loops, while cohesin passively diffuses along chromatin to tether sister chromatids. In budding yeast, the pericentric region is enriched in both condensin and cohesin. As in higher-eukaryotic chromosomes, condensin is localized to the axial chromatin of the pericentric region, while cohesin is enriched in the radial chromatin. Thus, the pericentric region serves as an ideal model for deducing the role of SMC complexes in chromosome organization. We find condensin-mediated chromatin loops establish a robust chromatin organization, while cohesin limits the area that chromatin loops can explore. Upon biorientation, extensional force from the mitotic spindle aggregates condensin-bound chromatin from its equilibrium position to the axial core of pericentric chromatin, resulting in amplified axial tension. The axial localization of condensin depends on condensin's ability to bind to chromatin to form loops, while the radial localization of cohesin depends on cohesin's ability to diffuse along chromatin. The different chromatin-tethering modalities of condensin and cohesin result in their geometric partitioning in the presence of an extensional force on chromatin.
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Affiliation(s)
- Josh Lawrimore
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Ayush Doshi
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Brandon Friedman
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Elaine Yeh
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Kerry Bloom
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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22
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Lacefield S. Chromosome Biology: Specification of the Kinetochore for Cohesin Recruitment. Curr Biol 2017; 27:R1319-R1321. [PMID: 29257967 DOI: 10.1016/j.cub.2017.10.056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Additional cohesin loaded at the centromere helps to facilitate proper chromosome segregation. A new study reveals the mechanism by which kinetochores recruit the cohesin loader to establish centromere cohesion.
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Affiliation(s)
- Soni Lacefield
- Department of Biology, Indiana University, Bloomington, IN, USA.
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23
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Lawrimore J, Friedman B, Doshi A, Bloom K. RotoStep: A Chromosome Dynamics Simulator Reveals Mechanisms of Loop Extrusion. Cold Spring Harb Symp Quant Biol 2017; 82:101-109. [PMID: 29167283 DOI: 10.1101/sqb.2017.82.033696] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
ChromoShake is a three-dimensional simulator designed to explore the range of configurational states a chromosome can adopt based on thermodynamic fluctuations of the polymer chain. Here, we refine ChromoShake to generate dynamic simulations of a DNA-based motor protein such as condensin walking along the chromatin substrate. We model walking as a rotation of DNA-binding heat-repeat proteins around one another. The simulation is applied to several configurations of DNA to reveal the consequences of mechanical stepping on taut chromatin under tension versus loop extrusion on single-tethered, floppy chromatin substrates. These simulations provide testable hypotheses for condensin and other DNA-based motors functioning along interphase chromosomes. Our model reveals a novel mechanism for condensin enrichment in the pericentromeric region of mitotic chromosomes. Increased condensin dwell time at centromeres results in a high density of pericentric loops that in turn provide substrate for additional condensin.
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Affiliation(s)
- Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, North Carolina 27599-3280
| | - Brandon Friedman
- Department of Biology, University of North Carolina at Chapel Hill, North Carolina 27599-3280
| | - Ayush Doshi
- Department of Biology, University of North Carolina at Chapel Hill, North Carolina 27599-3280
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, North Carolina 27599-3280
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24
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Abstract
Cohesin was identified through its major role in holding sister chromatids together. We are learning through analysis of cohesin and other members of the protein family (SMC [structural maintenance of chromosomes]) and their regulators that these ring complexes contribute to chromosome organization and dynamics throughout the cell cycle. We need to consider not only how ring complexes are regulated but how they interact with their fluctuating chromatin substrate.
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Affiliation(s)
- Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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25
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Hirano T, Nishiyama T, Shirahige K. Hot debate in hot springs: Report on the second international meeting on SMC proteins. Genes Cells 2017; 22:934-938. [PMID: 29067760 DOI: 10.1111/gtc.12539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 08/31/2017] [Indexed: 11/27/2022]
Abstract
The second international meeting on "SMC proteins: Chromosomal Organizers from Bacteria to Human" (SMC2017) was held in Nanyo City, Yamagata, Japan, from 13 to 16 June 2017. The meeting was attended by 134 participants (among them, 76 from outside of Japan) who were interested in one of the highly conserved classes of chromosomal proteins regulating large-scale chromosome structure and function. A keynote lecture was followed by 41 oral presentations and 71 poster presentations in the four-day meeting. Diverse topics surrounding eukaryotic SMC protein complexes (cohesins, condensins and SMC5/6) and prokaryotic SMCs, and a wide range of cutting-edge approaches (from polymer physics through medical genetics) were presented. Dominant themes discussed in the meeting included mechanistically how the SMC protein complexes might form chromatin loops and domains. The participants enjoyed both exciting debate about chromosome organization and warm welcome offered by local people in a small city located in the northern part of Japan.
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Affiliation(s)
| | - Tomoko Nishiyama
- Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan
| | - Katsuhiko Shirahige
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo, Japan
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26
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Herbert S, Brion A, Arbona JM, Lelek M, Veillet A, Lelandais B, Parmar J, Fernández FG, Almayrac E, Khalil Y, Birgy E, Fabre E, Zimmer C. Chromatin stiffening underlies enhanced locus mobility after DNA damage in budding yeast. EMBO J 2017; 36:2595-2608. [PMID: 28694242 PMCID: PMC5579376 DOI: 10.15252/embj.201695842] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 05/15/2017] [Accepted: 05/18/2017] [Indexed: 12/31/2022] Open
Abstract
DNA double-strand breaks (DSBs) induce a cellular response that involves histone modifications and chromatin remodeling at the damaged site and increases chromosome dynamics both locally at the damaged site and globally in the nucleus. In parallel, it has become clear that the spatial organization and dynamics of chromosomes can be largely explained by the statistical properties of tethered, but randomly moving, polymer chains, characterized mainly by their rigidity and compaction. How these properties of chromatin are affected during DNA damage remains, however, unclear. Here, we use live cell microscopy to track chromatin loci and measure distances between loci on yeast chromosome IV in thousands of cells, in the presence or absence of genotoxic stress. We confirm that DSBs result in enhanced chromatin subdiffusion and show that intrachromosomal distances increase with DNA damage all along the chromosome. Our data can be explained by an increase in chromatin rigidity, but not by chromatin decondensation or centromeric untethering only. We provide evidence that chromatin stiffening is mediated in part by histone H2A phosphorylation. Our results support a genome-wide stiffening of the chromatin fiber as a consequence of DNA damage and as a novel mechanism underlying increased chromatin mobility.
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Affiliation(s)
- Sébastien Herbert
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Alice Brion
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Jean-Michel Arbona
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Mickaël Lelek
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Adeline Veillet
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Benoît Lelandais
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Jyotsana Parmar
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - Fabiola García Fernández
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Etienne Almayrac
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Yasmine Khalil
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Eleonore Birgy
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Emmanuelle Fabre
- Equipe Biologie et Dynamique des Chromosomes, Institut Universitaire d'Hématologie, Hôpital St. Louis, Paris, France
- CNRS UMR 7212, INSERM U944, IUH, Université Paris Diderot Sorbonne Paris Cité, Paris, France
| | - Christophe Zimmer
- Unité Imagerie et Modélisation, Institut Pasteur, Paris, France
- CNRS UMR 3691, C3BI, USR 3756 IP CNRS, Paris, France
- Université Paris Diderot, Sorbonne Paris Cité, Paris, France
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27
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Abstract
At metaphase in mitotic cells, pulling forces at the kinetochore-microtubule interface create tension by stretching the centromeric chromatin between oppositely oriented sister kinetochores. This tension is important for stabilizing the end-on kinetochore microtubule attachment required for proper bi-orientation of sister chromosomes as well as for satisfaction of the Spindle Assembly Checkpoint and entry into anaphase. How force is coupled by proteins to kinetochore microtubules and resisted by centromere stretch is becoming better understood as many of the proteins involved have been identified. Recent application of genetically encoded fluorescent tension sensors within the mechanical linkage between the centromere and kinetochore microtubules are beginning to reveal - from live cell assays - protein specific contributions that are functionally important.
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Affiliation(s)
- Edward D Salmon
- University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Kerry Bloom
- University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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28
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Lawrimore J, Barry TM, Barry RM, York AC, Friedman B, Cook DM, Akialis K, Tyler J, Vasquez P, Yeh E, Bloom K. Microtubule dynamics drive enhanced chromatin motion and mobilize telomeres in response to DNA damage. Mol Biol Cell 2017; 28:1701-1711. [PMID: 28450453 PMCID: PMC5469612 DOI: 10.1091/mbc.e16-12-0846] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Revised: 03/28/2017] [Accepted: 04/18/2017] [Indexed: 12/13/2022] Open
Abstract
Mechanisms that drive DNA damage-induced chromosome mobility include relaxation of external tethers to the nuclear envelope and internal chromatin–chromatin tethers. Together with microtubule dynamics, these can mobilize the genome in response to DNA damage. Chromatin exhibits increased mobility on DNA damage, but the biophysical basis for this behavior remains unknown. To explore the mechanisms that drive DNA damage–induced chromosome mobility, we use single-particle tracking of tagged chromosomal loci during interphase in live yeast cells together with polymer models of chromatin chains. Telomeres become mobilized from sites on the nuclear envelope and the pericentromere expands after exposure to DNA-damaging agents. The magnitude of chromatin mobility induced by a single double-strand break requires active microtubule function. These findings reveal how relaxation of external tethers to the nuclear envelope and internal chromatin–chromatin tethers, together with microtubule dynamics, can mobilize the genome in response to DNA damage.
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Affiliation(s)
- Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Timothy M Barry
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Raymond M Barry
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Alyssa C York
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Brandon Friedman
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Diana M Cook
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Kristen Akialis
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jolien Tyler
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Paula Vasquez
- Department of Mathematics, University of South Carolina, Columbia, SC 29208
| | - Elaine Yeh
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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29
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Abstract
The centromere is an essential chromosomal locus that dictates the nucleation point for assembly of the kinetochore and subsequent attachment of spindle microtubules during chromosome segregation. Research over the last decades demonstrated that centromeres are defined by a combination of genetic and epigenetic factors. Recent work showed that centromeres are quite diverse and flexible and that many types of centromere sequences and centromeric chromatin ("centrochromatin") have evolved. The kingdom of the fungi serves as an outstanding example of centromere plasticity, including organisms with centromeres as diverse as 0.15-300 kb in length, and with different types of chromatin states for most species examined thus far. Some of the species in the less familiar taxa provide excellent opportunities to help us better understand centromere biology in all eukaryotes, which may improve treatment options against fungal infection, and biotechnologies based on fungi. This review summarizes the current knowledge of fungal centromeres and centrochromatin, including an outlook for future research.
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Affiliation(s)
- Steven Friedman
- Department of Biochemistry and Biophysics, Oregon State University, 2011 ALS Bldg, Corvallis, OR, 97331, USA
| | - Michael Freitag
- Department of Biochemistry and Biophysics, Oregon State University, 2011 ALS Bldg, Corvallis, OR, 97331, USA.
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30
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Abstract
The centromere is the genetic locus that specifies the site of kinetochore assembly, where the chromosome will attach to the kinetochore microtubule. The pericentromere is the physical region responsible for the geometry of bi-oriented sister kinetochores in metaphase. In budding yeast the 125 bp point centromere is sufficient to specify kinetochore assembly. The flanking region is enriched (3X) in cohesin and condensin relative to the remaining chromosome arms. The enrichment spans about 30-50 kb around each centromere. We refer to the flanking chromatin as the pericentromere in yeast. In mammals, a 5-10 Mb region dictates where the kinetochore is built. The kinetochore interacts with a very small fraction of DNA on the surface of the centromeric region. The remainder of the centromere lies between the sister kinetochores. This is typically called centromere chromatin. The chromatin sites that directly interface to microtubules cannot be identified due to the repeated sequence within the mammalian centromere. However in both yeast and mammals, the total amount of DNA between the sites of microtubule attachment in metaphase is highly conserved. In yeast the 16 chromosomes are clustered into a 250 nm diameter region, and 800 kb (16 × 50 kb) or ~1 Mb of DNA lies between sister kinetochores. In mammals, 5-10 Mb lies between sister kinetochores. In both organisms the sister kinetochores are separated by about 1 μm. Thus, centromeres of different organisms differ in how they specify kinetochore assembly, but there may be important centromere chromatin functions that are conserved throughout phylogeny. Recently, centromeric chromatin has been reconstituted in vitro using alpha satellite DNA revealing unexpected features of centromeric DNA organization, replication, and response to stress. We will focus on the conserved features of centromere in this review.
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Affiliation(s)
- Kerry Bloom
- Department of Biology, University of North Carolina at Chapel Hill, 623 Fordham Hall CB#3280, Chapel Hill, NC, 27599-3280, USA.
| | - Vincenzo Costanzo
- DNA Metabolism Laboratory, IFOM, The FIRC Institute of Molecular Oncology, Vai Adamello 16, 21139, Milan, Italy
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31
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Goloborodko A, Imakaev MV, Marko JF, Mirny L. Compaction and segregation of sister chromatids via active loop extrusion. eLife 2016; 5. [PMID: 27192037 PMCID: PMC4914367 DOI: 10.7554/elife.14864] [Citation(s) in RCA: 182] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 05/18/2016] [Indexed: 12/17/2022] Open
Abstract
The mechanism by which chromatids and chromosomes are segregated during mitosis and meiosis is a major puzzle of biology and biophysics. Using polymer simulations of chromosome dynamics, we show that a single mechanism of loop extrusion by condensins can robustly compact, segregate and disentangle chromosomes, arriving at individualized chromatids with morphology observed in vivo. Our model resolves the paradox of topological simplification concomitant with chromosome 'condensation', and explains how enzymes a few nanometers in size are able to control chromosome geometry and topology at micron length scales. We suggest that loop extrusion is a universal mechanism of genome folding that mediates functional interactions during interphase and compacts chromosomes during mitosis. DOI:http://dx.doi.org/10.7554/eLife.14864.001
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Affiliation(s)
- Anton Goloborodko
- Department of Physics, Massachusetts Institute of Technology, Cambridge, United States
| | - Maxim V Imakaev
- Department of Physics, Massachusetts Institute of Technology, Cambridge, United States
| | - John F Marko
- Department of Molecular Biosciences, Northwestern University, Evanston, United States.,Department of Physics and Astronomy, Northwestern University, Evanston, United States
| | - Leonid Mirny
- Department of Physics, Massachusetts Institute of Technology, Cambridge, United States.,Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, United States
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32
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Abstract
SMC (structural maintenance of chromosomes) complexes - which include condensin, cohesin and the SMC5-SMC6 complex - are major components of chromosomes in all living organisms, from bacteria to humans. These ring-shaped protein machines, which are powered by ATP hydrolysis, topologically encircle DNA. With their ability to hold more than one strand of DNA together, SMC complexes control a plethora of chromosomal activities. Notable among these are chromosome condensation and sister chromatid cohesion. Moreover, SMC complexes have an important role in DNA repair. Recent mechanistic insight into the function and regulation of these universal chromosomal machines enables us to propose molecular models of chromosome structure, dynamics and function, illuminating one of the fundamental entities in biology.
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